Conventionally, a semiconductor wafer made of a material such as silicon, gallium, arsenic or the like is produced with its large diameter scale and then cut and divided (diced) into device pieces, which are then transferred to a mounting step. In such a process, the semiconductor wafer, which is stuck to an adhesive sheet and held on it, is subjected to a dicing step, a cleaning step, an expanding step, a picking up step, and a mounting step, respectively. The dicing adhesive sheet generally comprises a plastic film base and an about 10 to 30 μm thick adhesive layer that is formed on the base and made of an acrylic adhesive or the like. For example, such an adhesive sheet that exhibits a peeling adhesion of about 1.5 to 6 N/25 mm to a silicon mirror wafer (sticking at 23° C. and peeling at 23° C.) is generally employed.
In the dicing process, the wafer is cut with a rotating and moving circular blade. A dominant cutting technique for such a process has been the so-called full-cut technique in which cutting is also performed on the inner part of the base of the dicing adhesive sheet that holds the semiconductor wafer.
When the semiconductor wafer is cut by the full-cut method using a conventional dicing adhesive sheet that has an about 10 to 30 μm thick adhesive layer and exhibits a peeling adhesion of about 1.5 to 6 N/25 mm, a crack called chipping can occur on the back side face of the semiconductor device (wafer). In recent years, as IC cards have become widely used, thin semiconductor devices have been developed and used. Chipping of such semiconductor devices can cause to a serious reduction in the strength of the semiconductor devices and cause to a significant reduction in reliability.
It is assumed that the mechanism of chipping in the dicing process should generally be as shown below. Referring to FIG. 2, in the full-cut process, a circular blade 3 cuts into a base film 11 of a adhesive sheet 1, so that an adhesive layer 12 or the base film 11 is pressed by the circular blade 3 to be deformed in the direction of the rotation and the forward direction. In such a process as shown in FIG. 2, separating occurs in a minute area (a) at the interface between the adhesive layer 12 and a semiconductor wafer 2 both being cut with the circular blade 3, so that the edge of the semiconductor wafer 2 is placed and left in the space. As a result, the rotation of the circular blade 3 causes the cut portion of the semiconductor wafer 2 to irregularly vibrate during the cutting process. It is assumed that such irregular vibration of the body interferes with the normal cutting process so that chipping can occur.
For example, Japanese Patent Laid-Open No. H05-335411 (1993) discloses a technique (Dicing Before Grinding Process) for solving such a problem. The proposed process includes the steps of performing dicing to form grooves with a certain depth in a semiconductor wafer in which devices have been formed and then back-grinding the wafer (grinding the back surface of the wafer) to the bottom of the grooves formed by dicing, so that thin semiconductor device pieces are produced. Such a process can suppress chipping. In a transferring step before the back-grinding step, however, the semiconductor wafer can easily break at the cut portions, which have been formed with a depth of several tens to hundreds μm in the semiconductor wafer by dicing. Therefore, such a process can reduce the production yield with respect to the semiconductor wafer.
It is an object of this invention to solve the above problems with the prior art and to provide a dicing adhesive sheet, wherein the production yield of a deiced body such as a semiconductor wafer is high, and chipping during the dicing is prevented.
It is another object of this invention to provide a dicing method using such a dicing adhesive sheet.